Structural behaviour of R/C beams exposed to natural fires

The inherent fire resistance of concrete makes a complete collapse of R/C structures in fire a rare event. In recent years, however, some cases were reported where failure took place after the maximum ambient temperature had been reached, i.e. during the cooling phase. The present work is aimed at the investigation of the structural behaviour of reinforced concrete beams under the effect of natural fires, which are characterized by heating and cooling down phase. To this aim, the present constitutive models proposed in Eurocode 2 are suitably modified, in order to account for the intrinsic issues regarding the materials’ behaviour during the cooling phase. A 3D finite element model of a fire exposed R/C beam was developed in ABAQUS software, taking into account as many realistic parameters as possible. The model was validated against the available experimental results and the agreement between the numerical and experimental results is satisfying. A parametric study is carried out, in order to identify the critical parameters governing the R/C beam fire response. Results show that parameters such as duration of heating and cooling phase, beam size, as well as concrete cover depth play a crucial role in the magnitude of the residual displacements and the amount of recovery upon cooling.